The invention relates to a filter insert which is received exchangeably by a shaft along a channel and which can be fixed sealingly relative to the frame shaped shaft walls via at least one gasket preferably continuous on the flow-off side.
A filter arrangement of this type with a filter which can be pulled off upwards is disclosed by German Published, Unexamined Patent Application 3,317,851. Since, in practice, unfiltered air which can pass through between the filter and the associated channel wall must reliably be prevented from entering the interior, a filter receptacle consisting of two frames spaced from one another is used. The frames are connected sealingly to the channel wall and surround an upwardly open shaft which can be closed by a removeable cover and which receive the filter. In this arrangement, a continuous gasket, against which the filter is Pressed, is intended to prevent leakage air bypassing the filter from passing between the latter and the frame and into the passenger space.
If, in this respect, a high pressure force is adopted to obtain a good sealing effect, considerable effort is required to change the filter and there is the danger that the gasket will be damaged. A lower pressure force, although making the exchange operation easier and reducing the danger of damage to the gasket, nevertheless decreases the protection against leakage.
An object of the present invention it to provide an arrangement making it possible to change the filter easily and, at the same time, ensuring that unfiltered air is prevented from overflowing into the passenger space during the operation of the filter.
This object and other objects are achieved according to advantageous embodiments of the present invention by providing a pressing element for forming a gap between a gasket and associated bearing surface as a result of a reduction of pressure in the Pressing element during removal of the filter. This allows the filter to be changed without damaging the gasket A higher pressure which thereafter takes effect again, and which can be above atmospheric pressure or correspond to this, guarantees, during filter operation, that the gasket bears sealingly against the associated sealing surface.
At the same time, the pressing element can be arranged on a side opposite the continuous gasket, so that it merely gives rise to a shifting movement in the direction of extension of the channel.
In a preferred exemplary embodiment of the invention, the pressing element is designed as a substantially continuous tube which is made of elastic material and which one end is closed, another end of which is equipped with a connection piece.
It is also possible, however, to design the pressing element as a hollow chamber closed on itself, with a connection piece leading away from it.
In such an embodiment of the pressing element, wall regions of the hollow chamber can be formed by fixed wall parts especially on the same side as the filter. The channel thus created can then be bridged by a diaphragm-like sealing element.
If the pressing element is designed as a hollow chamber closed on itself, to simplify the construction, the pressing element can perform the function of the gasket.
For an especially stable design of the pressing element, this can be arranged on the shaft. Another advantage of this is that, when the filter is being changed the line leading to the pressure reducing device does not have to be detached.
The filter can be divided transversely relative to the direction of flow and the pressing element be received by a groove of the division. This design makes it possible in a simple way to connect a dust filter and an absorption filter in series.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.